function User(firstName, lastName) {
  this.firstName = firstName;
  this.lastName = lastName;
  this.fullName = firstName + lastName;
}

// 能否不使用new，通过User函数创建对象（不能更改User函数）
var obj1 = {
    firstName: 'zeng',
    lastName: 'kingsen'
}


User.call(obj1,obj1.firstName,obj1.lastName)

console.log(obj1.fullName);




/* 老师的写法 */
var u = {}
User.call(u,'li','xin')
console.dir(u);